Electro-magnetic waves in the millimeter and sub-millimeter wave frequency range, from 100 to 1000 GHz, are being utilized in fast-scan rotational spectroscopy for detection and identification of gas molecules. This technique is used for monitoring indoor air quality, gas leaks, human breath, and others for a wide variety of medical, security, and safety applications. Advances of the high frequency capability of CMOS have made it possible to consider CMOS as an affordable means for implementing the electronics for these spectroscopy systems, in which a signal generation circuit operating at 100 GHz and higher with an ultra-wide frequency tuning range, approximately 50%, is a key component. The rotational spectroscopy application is particularly well suited for CMOS implementation because it requires only a few micro-watt of transmitted power to avoid the saturation of molecules. This is significantly different from communication or radar applications in which high transmitted power is needed.
Recently, numerous millimeter-wave CMOS signal generation circuits/LC oscillators have been reported. These circuits are categorized into three groups based on their focus. The first group generates signals at frequencies as high as possible. For example, a 300-GHz fundamental mode VCO in 65-nm CMOS demonstrated that the fundamental oscillation frequency of an oscillator approaches the fmax of technology. By employing a frequency multiplication technique in conjunction with an oscillator, signals are generated beyond fmax. As another example, 553-GHz signal was generated by using a 4-push technique in 45-nm CMOS. The second group increases the tuning range while minimizing phase noise degradation. For example, a 57.5-90.1 GHz oscillator with a 44% tuning range was achieved by using a magnetically-tuned multi-mode technique. The third group is focused on increasing the output power. For example, a 283-to-296-GHz VCO in 65-nm CMOS with 0.76 mW peak output power has been demonstrated. Using a triple-push technique, the output power of this CMOS signal generation circuit is significantly improved near the sub-millimeter wave frequencies.
However, all reported wide tuning millimeter wave CMOS signal generation circuits with a frequency tuning range larger than 20% operate below 90 GHz. At 100 GHz, the tuning range has been limited to less than 11%, which is far below the desired range. Therefore, there is a need in the art to dramatically increase the tuning range of signal generation circuits with output frequency greater than 100 GHz. There is a need in the art for a CMOS signal generation circuit having an approximately 50% frequency tuning range without a frequency gap.